1. Field of the Invention
The present invention relates generally to an antenna switching module for transmitting/receiving RF signals through a single antenna in a mobile terminal, and more particularly to an antenna switching module having an amplification function, in which the power amplification of a transmission signal is performed together with the switching of transmission/reception signals to an antenna.
2. Description of the Prior Art
Generally, mobile terminals, such as cellular phones or Personal Digital Assistants (PDAs), are devices for transmitting/receiving data or voice signals through Radio Frequency (RF) channels without limitation of place. Most of mobile terminals employ a construction in which only a single antenna is mounted and transmission and reception terminals on a printed circuit board are alternately connected to the antenna, in consideration of external appearance or size restrictions.
Recently, with the miniaturization of mobile terminals, the development of RF parts for mobile terminals aims at miniaturization, modulization, and multi-function. Therefore, RF circuits connected to an antenna have been realized as modules. Of the modules, there is provided an Antenna Switching Module (ASM) in which a circuit, connected to the antenna to alternately switch the connections between two signals and the antenna, is realized as a module. Further, a Front End Module (FEM) in which a saw filter is further included at a side of a reception terminal of the ASM to filter a reception signal has been developed. Moreover, an attempt has been made to integrate the ASM and a Power Amplifier Module (PAM) for amplifying the power of a transmission signal to a transmission level into a single module.
FIGS. 1 and 2 are views showing the constructions of conventional antenna switching modules. As shown in FIGS. 1 and 2, each of antenna switching modules fundamentally comprises a low pass filter 11 or 21, a first switching diode 12 or 22, a transmission line 13 or 23, and a second switching diode 14 or 24. Each of the low pass filters 11 and 21 eliminates harmonic frequency components included in a transmission signal received from a transmission terminal TX. Each of the first switching diodes 12 and 22 connects or disconnects a transmission signal path from the transmission terminal TX to an antenna terminal ANT. Each of the transmission lines 13 and 23 connects between the antenna terminal ANT and a reception terminal RX and has a length of λ/4 (λ: wavelength of a reception signal). Each of the second switching diodes 14 and 24 connects or disconnects a reception signal path from the antenna terminal ANT to the reception terminal RX.
In the above constructions, depending on the connecting directions of the first and second switching diodes 12, 14, 22 and 24, constructions required to apply a control signal Vc for controlling on/off states of the first and second switching diodes 12, 14, 22 and 24, are different, as shown in FIGS. 1 and 2.
That is, in case of the antenna switching module of FIG. 1, if a high level control signal Vc is applied to an anode of the first switching diode 12, the first switching diode 12 is turned on, and the second switching diode 14 whose cathode is grounded is also turned on. At this time, a path ranging from the transmission terminal TX to the antenna terminal ANT through the low pass filter 11 is formed with respect to a transmission signal. Further, a path ranging from the antenna terminal ANT to the ground through the transmission line 13 is formed with respect to a reception signal. Therefore, the transmission signal is transmitted through the antenna terminal ANT, and the reception signal is bypassed to the ground and is not transferred to the reception terminal RX.
On the other hand, if a low level control signal Vc is applied to the anode of the first switching diode 12, the first and second switching diodes 12 and 14 are turned off, so the path between the antenna unit ANT and the transmission terminal TX is disconnected, and a path ranging from the antenna terminal ANT to the reception terminal RX is formed. Therefore, a reception signal received through the antenna terminal ANT is transferred to the reception terminal RX through the transmission line 13.
Further, in case of the antenna switching module shown in FIG. 2, if a high level control signal Vc is applied to an anode of the second switching diode 24, the second switching diode 24 and the first switching diode 22 are turned on, so a signal path ranging from the transmission terminal TX to the antenna terminal ANT is formed. At this time, a reception signal is bypassed to the ground and is not transferred to the reception terminal RX. On the contrary, if a low level control signal Vc is applied to the anode of the second switching diode 24, the second and first switching diodes 24 and 22 are turned off, so a signal path ranging from the antenna terminal ANT to the reception terminal RX is formed. In this case, each of the low pass filters 11 and 21 performs the functions of eliminating unnecessary harmonic frequency components generated from a power amplifier module (not shown) located at its previous stage and transmitting only a transmission signal to the antenna terminal ANT. The transmission lines 13 and 23 are tuned to reception frequency bands to prevent a high power transmission signal from flowing into the reception terminal RX.
Therefore, a mobile terminal equipped with the antenna switching module having the above construction applies a clock signal in which a mark and a space appear to the antenna switching module as a control signal (Vc) to operate transmission and reception modes in a time division manner, thus performing transmission and reception.
If these conventional antenna switching modules are used, a mobile terminal must prepare an additional power amplifier module for amplifying a transmission signal at a previous stage of a transmission terminal of the antenna switching module, which hinders the miniaturization of mobile terminals.
Therefore, attempts to implement the antenna switching module and the power amplifier module as a single part have been made.
As one of such attempts, FIG. 3 is a view showing a conventional module in which the ASM and the PAM are implemented as a single package. In this case, respective ASM and PAM circuits are mounted on a single Low Temperature Co-fired Ceramic (LTCC) board while the constructions of a conventional PAM 32 and a conventional ASM 31 are maintained as they are, thus implementing the conventional module of FIG. 3.
In the conventional module, it is difficult to expect a size reduction effect, because the PAM and the ASM are merely implemented as a single package, but the conventional PAM and ASM circuits are maintained as they are.